The fouling of marine structures by organisms in sea water has been a major problem for virtually centuries. These structures, such as ship hulls, buoys, and pilings, are fouled by the viscous bio-organic products and absorbed organic matter from microorganisms present in the water. Fouling of the structures occurs both in sea water and fresh water. It also occurs in industrial water systems such as cooling systems.
The initial organisms in this fouling process are bacteria present in the aqueous environment followed by biotic progression of diatoms, hydrids, algea, bryozoans, and macrofoulants. The obvious result of this biological activity is the production of a tenacious, opaque slime which forms on the submerged surfaces. Macrofoulants, such as barnacles, form preferentially on roughened surfaces.
Fouling of marine structures is a problem of major proportions. For example, fouling of a boat hull significantly reduces its speed and increases its fuel consumption. Buoys can shift position or become less detectable due to the excessive weight of fouling organisms.
Industrial water systems are plaqued by fouling problems associated with marine growth. The water side of heat exchangers are adversely affected by fouling organisms such that flow rates are lessened and heat transfer efficiency seriously decreased. The fouling of piping in water-intake systems for water cooled marine engines is well known. In such cases, cooling ability is adversely affected, valve damage results, and water pumps are corroded. Corrosion rates of associated piping is accelerated by the presence of these fouling organisms.
Perhaps the most popular method of preventing fouling of marine structures has been the use of copper cladding, and, in some cases, poisonous paints. An asphalt coating has been used effectively. Also, coatings containing organometallic salts, such as tri-n-butyl tin oxide, are extremely effective in killing these organisms. The U.S. Navy apparently has found that coatings containing copper salts and oxides, e.g. cuprous oxide, are effective anti-fouling coatings. More recently, the use of polymeric organotin compounds in coating compositions or paints has received widespread attention.
However, it has been found that all of these prior efforts have serious commercial drawbacks. Most of these prior coating compositions are susceptible to leaching, either intentionally for effective growth control, or inadvertently due to solubility factors. In either case, the leaching phenomenon causes a serious pollution problem for the surrounding waters.
One of the more promising prior coating compositions has been polymeric compounds containing organotin ingredients. For example see Leebrick, U.S. Pat. No. 3,167,473, Goto, et al, U.S. Pat. No. 3,684,752, Dyckman, et al, U.S. Pat. Nos. 3,979,354 and 4,082,709. However, none of these prior efforts have met with commercial success. All of these coating compositions are deficient by exhibiting very poor adhesion characteristics to the submerged marine structure; all exhibit unacceptable softness of the film, particularly when applied in multiple coats; all have unacceptable abrasion resistance against moving water; and all result in unacceptable leaching rates, e.g., are short lived and/or are pollutants.
Therefore, it would be desirable to provide a new and improved marine anti-fouling coating composition which has a smooth hard surface, which is non-leaching, and which is cost effective for commercial production and application.